The present invention relates to a stabilized solid pesticidal composition containing acephate.
Acephate (O,S-dimethyl acetylphosphoramidothioate) is an insecticidally active compound as described in the page 1 of The Pesticide Manual 8th edition (published from the British Crop Protection Council in 1987). Since this compound is effective to control various pests, it is now used as an active ingredient for agricultural pesticides.
However, acephate in pesticidal compositions is not so high in its stability, so that acephate in the compositions decomposes violently depending upon storage conditions. As a result, there is a case where the pesticidal activity of acephate cannot be used effectively.
Therefore, there has been a demand for the development of stabilized pesticidal compositions containing acephate.
The present invention is based on the discovery that solid pesticidal compositions containing acephate may be stabilized by adding thereto at least one of boron oxide, metaboric acid, aluminum oxide and the calcined product of synthetic silicon dioxide. The present invention provides a stabilized solid pesticidal composition containing acephate and a method for stabilizing the composition.
The amount of at least one boron oxide, metaboric acid and aluminum oxide effective to stabilize acephate is generally 0.01 to 0.5 part by weight to 1 part by weight of acephate. Of course, a higher amount thereof may be used.
When the calcined product of synthetic silicon dioxide is used as the stabilizer, the amount of the stabilizer added is generally 0.05 part by weight or more to 1 part by weight of acephate.
The calcined product of synthetic silicon dioxide used in the present invention is usually produced by adding a mineral acid such as hydrochloric acid and sulfuric acid to an aqueous sodium silicate solution to sodium silicate solution to precipitate synthetic silicon dioxide and then calcining this precipitate at 600xc2x0 C. to 900xc2x0 C., preferably 700xc2x0 C. to 800xc2x0 C. Commercially available products such as Carplex CS-7 (produced by Shionogi and Co., Ltd.), Carplex CS-5 (produced by Shionogi and Co., Ltd.) and Finesil P-8 (produced by Tokuyama Soda Co., Ltd.) may be used as they are.
The solid pesticidal composition stabilized by the present invention usually contains (a) acephate, (b) at least one boron oxide, metaboric acid, aluminum oxide and the calcined product of synthetic silicon dioxide and (c) a solid carrier for formulation. When the calcined product of synthetic silicon dioxide is used as the stabilizer, these stabilizers may be used as a solid carrier for formulation.
The content of acephate in the above solid pesticidal composition is generally 0.5 to 99 wt. %, preferably 5 to 95 wt. %, and the content of boron oxide, metaboric acid and/or aluminum oxide used as the stablizer, is an amount sufficient to stabilize acephate, i.e. usually 0.01 to 50 wt. %, preferably 0.1 to 20 wt. %, more preferably 1 to 10 wt. %.
When the calcined product of synthetic silicon dioxide is used as the stabilizer, the content of acephate in the solid pesticidal composition stabilized by the present invention is generally 0.5 to 99 wt. %, preferably 5 to 95 wt. %, and the content of the calcined product of synthetic silicon dioxide used is an amount which can stabilize acephate, usually 1 to 99 wt. %.
The solid carrier for formulation used in the present invention includes inorganic carriers such as kaolin clay, attapulgite clay, sericite clay, pyrophyllite clay, montmorillonite clay, zeolite, bentonite, acid clay, activated clay, serpentine, talc and diatomaceous earth, inorganic salts such as sulfates, nitrates and chlorides and synthetic carriers such as silica; and organic carriers such as sugars, starch, dextrin, flour, soybean powder, corn powder, and wood powder. These solid carriers for formulation are contained in the solid pesticidal composition of the present invention in an amount of usually 1 to 90 wt. %, preferably 20 to 70 wt. %.
If necessary, the above solid pesticidal composition may further contain various kinds of auxiliary for pesticidal composition. The auxiliary for pesticidal composition includes surface active agents, coloring agents, perfumes, known stabilizers and the like. These auxiliaries may be contained in the solid pesticidal composition of the present invention in an amount of usually 0.1 to 35 wt. %, preferably 2 to 10 wt. %.
The surface active agents include for example anionic surface active agents such as the salt of alkyl sulfate (e.g. sodium lauryl sulfate), alkylarylsulfonates (e.g. sodium alkylnaphthalenesulfonate), lignosulfonates (e.g. sodium lignosulfonate), succinic acid ester derivatives, the salt of the ester of polyethylene glycol alkylaryl ether with sulfuric acid and aromatic sulfonate/formaldehyde condensates, and nonionic surface active agents such as polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, and polyoxyethylene arylaryl ether.
The above solid pesticidal composition may further contain other active ingredients, for example, pyrethroid compounds such as fenpropathrin and fenvalerate.
The above solid pesticidal composition may be produced according to the conventional methods, for example, by admixing acephate, stabilizer, solid carrier for formulation and if necessary auxiliaries for formulation such as surface active agents in a mixer, and pulverizing the mixture with a pulverizer, for example, air mills, hammer mills or centrifugal pulverizers or by molding the resulting pulverized product into granules with compression molding presses, e.g., roller compacters, extrusion granulators and pan granulators.